1. Field of the Invention
The invention relates to on-line monitoring of combustion turbines for defects. More specifically, the invention is an apparatus and method for monitoring acoustic signals within a combustion turbine to monitor the passage of foreign particles through the turbine on-line.
2. Description of the Related Art
Combustion turbines typically operate at extremely high temperatures, for example, 2500xc2x0 F. to 2900xc2x0 F. (1371xc2x0 C. to 1593xc2x0 C.). Such high temperatures will cause failure of various components unless they are protected from the heat. These components include the rotating blades of the turbine, and the vanes for directing gas flow within the turbine. A typical combustion turbine will have three to four rows each of blades and vanes, with approximately 50 to 100 blades or vanes per row, and will typically have approximately 500 total blades and vanes to protect. A commonly used material for vanes and blades is nickel-cobalt. These components are usually insulated by a thermal barrier coating to enable their use within high temperature environments. A typical thermal barrier coating is yttria-zirconia.
Currently, it is necessary to periodically stop the turbine and inspect the components for deterioration of the thermal barrier coating, defects in other coatings, or other defects, for example, formation of cracks. It would be desirable to monitor the condition of these components while the turbine is in use. Avoiding the need to periodically stop the turbine for inspection reduces downtime, increasing the turbine""s efficiency. Similarly, early detection of defects reduces repair costs and outage time, again increasing turbine efficiency. A need exists for monitoring conditions within the turbine that can cause defects, or are a symptom of a defect, such as foreign objects passing through the combustion turbine.
One proposed system for detecting and locating defects within turbine components involves using a probe on the housing of the turbine to measure the acoustic spectrum of the turbine. This acoustic spectrum is then compared with a reference spectrum, with deviations from this reference spectrum indicating a damaged turbine blade or component. Preferred embodiments of this method include generating an acoustic signal to increase the intensity of the acoustic spectrum within the turbine.
Another proposed system is for monitoring synchronous blade vibration. The system includes at least three sensors circumferentially arranged around a row of blades. The sensors may be of the eddy current type, microwave, or optical. The sensors detect the arrival time of each blade at the sensor, using the difference between the expected arrival time of the blade and the actual arrival time of the blade to determine the amplitude of the blade vibration. This information has been analyzed using Fourier transforms to determine the vibratory stress on each blade.
Yet another proposed system for monitoring the condition of a turbine includes mounting an acoustic emission sensor on a surface of an engine component. The sensor will detect the resulting acoustic emissions when particles of debris strike the surface to which it is mounted or other surfaces.
One proposed method utilizes ultrasonic inspection of rotating machinery while the machinery is in operation. The method uses an ultrasonic transducer to radiate pulses of ultrasonic energy at a frequency substantially equal to a subharmonic of the frequency of the turbine rotation. The transducer will sense reflections of the ultrasonic pulses from the blade, and convert the reflections into an electrical signal. Changes in the reflected signal can indicate a damaged blade.
Another system for monitoring the intake of foreign objects into an engine includes sensors positioned near the engine intake and exhaust duct for detecting electrostatic charges induced in the sensors by passing foreign bodies. Each sensor includes a plurality of sensor elements, with each sensor element having an insulating layer of epoxy resin and the charge-collecting layer of silver-loaded epoxy resin.
Accordingly, there is a need for an apparatus and method for detecting the passage of foreign debris through a combustion turbine, measuring the frequency and intensity of the resulting acoustic signals and displaying such information on line, and recording this information, thereby providing an indication of when a turbine needs to be shut down for maintenance.
The invention is a system for monitoring the frequency and severity of impacts from foreign debris upon various components within a combustion turbine during operation of the turbine. The system relies on the detection of acoustic signals generated by the impact of foreign debris upon various components of the turbine.
An acoustic sensor, such as an acoustic waveguide, is bonded to a suitable location on the combustion turbine. This location may be either inside or outside of the gas turbine, with one example location being adjacent to one of the vanes within the turbine. The other end of the waveguide is bonded to a transducer, for example, a bender transducer, for converting the acoustic signal into an electric signal.
The electrical signal may then be transmitted to a radio frequency step-up transformer for ensuring that even the smallest voltages received are increased to at least approximately 1.5 volts. Lastly, the electrical signal is transmitted to a capacitive voltage divider, transmitting the voltage to one or more light-emitting diodes (LED), depending upon the voltage received. Smaller voltages will light only one LED, whereas larger voltages will light an increasing number of LEDs. For example, a voltage between 1.5 and 2.5 volts may light a green LED, a voltage between 2.5 and 4.5 volts may light a green plus a yellow LED, and a voltage exceeding 4.5 volts may light a green, yellow and red LED.
The received signal may also be recorded for further study using a data logger or a storage oscilliscope. For example, a video camera may record the activation of the LEDs, recording the information on a videocassette, and displaying it on a video screen.
Alternatively, instead of a narrow band [xcx9c3 kHz] bender transducer, a wide band [xcx9c0.1 to 1 Mhz] transducer may be bonded to the AWG and the acoustic pulse from FOD measured and stored. Once the information is stored, the spectrum signature may be obtained from Fourier analysis. The spectrum signatures from the impact of various objects, such as ceramic chips and metal chips, will be different, allowing for their identification. Certain spectrum signatures, for example, those indicating a chip from a turbine blade, will indicate that it is desirable to shut down the combustion turbine for maintenance.
A sensing system of the present invention can collect and record information about the number and magnitude of foreign object impact within the combustion turbine, and transmit this information over long distances, without power supplies or batteries.
It is therefore an aspect of the present invention to provide a foreign object impact sensor capable of detecting the acoustic signal resulting from a wide variety of foreign objects impacting components within a combustion turbine.
It is another aspect of the present invention to provide a foreign object impact sensor capable of displaying and recording the frequency and severity of foreign object impacts within the combustion turbine.
It is a further aspect of the present invention to provide a foreign object impact sensor providing a means to record and store signals from foreign object impacts, so that a spectrum signature can be obtained from Fourier analysis.
It is another aspect of the present invention to provide a foreign object impact sensor capable of being set up and utilized at minimal cost.
These and other aspects of the invention will become apparent through the following description and drawings.